As a recording method using an ink-jet printer, various kinds of diverse ink jetting systems have been developed, and for recording in these systems, ink droplets are generated and deposited to various recording materials (paper, film, cloth etc.). The recording method using an ink-jet printer is characterized in that because a recording head is not contacted with a recording material, the method is silent without generating sounds, and can without limitation print on uneven surfaces, soft materials, easily broken products, etc. Because of its features such as downsizing printers, higher speed and easy coloration, this recording method has spread rapidly in recent years, and is expected to expand significantly in the future. Images and literal information on a color display in a computer, when recorded in color by an ink-jet printer, are expressed generally by subtractive mixed colors using 4 color inks of yellow (Y), magenta (M), cyan (C) and black (K). To reproduce a subtractive mixed color image as faithfully as possible by a subtractive mixed color image of red (R), green (G) and blue (B) for CRT displays etc., it is desired that coloring matters used, particularly coloring matters used in YMC inks, have hues as near as possible to standard hues of YMC and are as vivid as possible. It is also desired that the ink composition is stable during storage for a long period, provides printed images with high density, and is superior to fastness such as water resistance, light resistance, moisture resistance, weathering resistance, ozone-gas resistance etc.
Weathering resistance refers to fastness in airy shades. Generally, when a coated paper called a glossy paper is printed and left in airy shadows for a long time, discoloration and fading often occur. The reason for such discoloration and fading is not definitely elucidated at present, however it is estimated that an interaction of ozone gas, oxidizing gases such as SOx, NOx etc. in the air with inorganic materials and/or polymers applied onto the processed paper causes the discoloration and fading of coloring matters. The coated paper to be used in exhibits such as posters etc. in various fields will be exposed to lights (electric lights, fluorescent lamps, sun rays etc.) in many cases, and thus there is demand for an ink composition excellent particularly in light resistance.
The ink-jet printer is used in broader fields ranging from small printers for OA to large printers in industry, and is desired to have higher fastness such as water resistance, light resistance, moisture resistance etc. than in the past. Water resistance and moisture resistance are under significant improvement by coating, together with PVA resin, organic or inorganic fine particles (e.g. cationic polymer, porous silica, alumina sol and special ceramics) capable of adsorbing coloring matters in ink, onto the surface of the paper. Various coated papers for ink-jet printers have been commercially available, and some coated papers are significantly improved. For improving light resistance, however, there has been no established technique, and improvement thereof is an important task. In recent years, an opportunity to print photographs is increasing because of improvements in printing qualities of ink-jet printers, and the coated paper (called a glossy paper) used in printing photographs has the problem of discoloration and fading attributable to gases, particularly an ozone gas, in the air. The respective dyes of yellow, magenta, cyan and black are faded at different levels, and it is an important task in recent years to improve the ozone-gas resistance of the respective colors during long-term storage and to uniformalize the fading levels of the respective colors by an ozone gas.
As a typical skeleton of a yellow coloring matter used in an aqueous ink for ink-jet recording, an azo dye is used. Some azo dyes used at present are excellent in hue and water resistance, but the azo dye is generally inferior in light resistance. The azo dye is inferior in light resistance to dyes such as cyan dyes, typically copper phthalocyanine dyes. However, a large number of yellow coloring matters are very excellent in ozone-gas resistance, thus allowing the fading of magenta, cyan and black to be remarkable in photographic printing. As a means to solve this problem, a dye having ozone-gas resistance in harmony with other colors is desired as the yellow coloring matter. The yellow coloring matters used at present cannot simultaneously satisfy hue, clarity, light resistance, water resistance, humidity resistance, ozone-gas resistance and dissolution stability.
The object of the present invention is to provide an aqueous ink composition which has a hue and clarity suitable for ink-jet recording, provides a recorded matter with high fastness such as light resistance and humidity resistance, and can regulate ozone-gas resistance in the magenta, cyan and black levels, as well as a water-soluble dye composition very excellent in shelf stability and a yellow coloring matter suitable therefor.